Engine exhaust turbine inlet screen

ABSTRACT

An engine exhaust turbine inlet screen exposed in normal operation to substantial variations in exhaust gas temperatures is supported in the exhaust gas flow path by a bracket connected with the central portion of the screen by a combination of stiff and flexible portions of minimum mass. The arrangement provides free expansion of the screen, minimizing of internal stresses due to heat transfer between the screen and bracket and isolation of residual stresses due to heat transfer to the small central portion of the screen.

United States Patent 1191 Addie et al. May 29, 1973 [54] ENGINE EXHAUST TURBINE INLET 2,437,138 3/1948 Theis ..415/121 G SCREEN 3,352,104 11/1967 Duerr ..60/13 [75] Inventors: Albert N. Addie, La Grange Park; Examiner Al Lawrence Smith Glen woodndge both Assistant Examiner-Warren Olsen of v AttorneyJ. L. Carpenter and Robert J. Outland [73] Assignee: General Motors Corporation, Dfitl'Oit, Mich. [22] Filed: May 6, 1971 v An engine exhaust turbine inlet screen exposed in nor- [211 App! 140301 mal operation to substantial variations in exhaust gas v temperatures is supported in the exhaust gas flow path [52] US. Cl. ..60/13 R, 55/385, 55/503, by a ra ket connected with the central portion of the 55/511, 60/3909 DP, 415/121 G screen by a combination of stiff and flexible portions [51] int. Cl ..F02b 37/04 of minimum mass. The arrangement provides free ex- [58] Field of Search .55/490, 509, 385, pansion of the screen, minimizing of internal stresses 55/503; 60/3909 R, 39.09 P, 13; 415/121 G due to heat transfer between the screen and bracket and isolation of residual stresses due to heat transfer [56] References Cited to the small central portion of the screen.

UNITED STATES PATENTS 3 Claims, 4 Drawing Figures 3,286,459 11/1966 Ephraim ..60/13 ENGINE EXHAUST TURBINE INLET SCREEN BACKGROUND OF THE INVENTION This invention relates to engine exhaust turbine inlet screens for protecting the exhaust turbine against the entry of potentially damaging foreign matter and, more particularly, to an inlet screen assembly constructed in a manner to minimize internal stresses in the screen that could be caused by the varying exhaust gas temperatures of engine operation.

US. Pat. No. 3,286,459 Ephraim Jr. assigned to the assignee of the present invention discloses in FIGS. 1 3 an engine exhaust turbine inlet screen arrangement. In this arrangement, the screen is formed of a perforated metal plate and is supported within a housing defining the exhaust gas flow path by a support member having a plurality of flexible fingers secured around the outer periphery of the screen. The flexible mounting of this arrangement permits the screen to expand and contract due to changes in its temperature without substantial restraint from the mounting.

While this arrangement of US. Pat. No. 3,286,459 represents a substantial improvement over screens with edge constraining mountings, it has been found through experience that the arrangement does not completely solve the problem of failures due to cracking. Such failures usually occur near the edge of the screen after an extended period of service. Testing of structures according to this arrangement indicated that substantial temperature gradients are present in the screen during changes engine power, which it was concluded are a result of the heat sink efiect provided by the screen upp The heat sink efiect has the result of providing a heat flow path which tends to slow changes in screen temperature at the edges as compared to the central portions of the screen. The temperature variation between inner and outer screen portions acts as a constraint to the uniform growth of the screen during temperature changes, resulting in internal stresses which, after a sufficient number of temperature cycles result in failure of the highly stressed screen edge portions.

SUMMARY OF THE INVENTION The present invention provides an engine exhaust turbine inlet screen assembly which is an improvement over the prior arrangement, while retaining certain advantages thereof. Like the prior arrangement, the present invention utilizes a screen, preferably formed of a perforated metal plate, to prevent the passage of foreign matter, such as broken valve parts, into the turbine. The screen is supported within a housing with radial clearance around its edges to permit free expansion of the screen relative to the housing. In addition, the means for supporting the screen utilizes resilient fingers to permit unrestrained expansion of the screen.

Unlike the previous arrangement, the screen of the present invention is connected with its support means only at points relatively close to its center so that the constraining effect of temperature differentials due to heattransfer' to the support takes place in a much smaller area. In addition, the mass of the supporting means where it contacts the screen is significantly reduced so that heat transfer between the screen and support is severely limited. In this way, localized temperature differentials in the screen during transient power conditions are minimized, as are internal stresses in the screen resulting therefrom.

These and other features and advantages of the invention will be more clearly understood from the following description of a preferred embodiment of the invention, taken together with the accompanying drawmg.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a fragmentary plan view of an internal combustion engine having an exhaust driven turbosupercharger wherein the turbine is protected by an inlet screen assembly according to the invention;

FIG. 2 is a cross-sectional view of the turbine inlet screen assembly utilized in the engine of FIG. 1;

FIG. 3 is an end view of the screen assembly of FIGS. 1 and 2 as viewed from the plane indicated by the line 3-3 of FIG. 2 looking in the direction of the arrows; and

FIG. 4 is a fragmentary cross-sectional view of the screen assembly taken in the plane indicated by the line 44 of FIG. 2, as viewed in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1 of the drawing, there is shown an internal combustion engine generally indicated by numeral 10 and including an exhaust manifold 12 and a turbocharger 14 adapted to be driven by exhaust gases discharged by the engine 10 through manifold 12. The turbocharger (also known as a supercharger or turbosupercharger) operates in known manner to compress the inlet air delivered to the engine and includes an exhaust gas-driven turbine fed through an inlet scroll 16 which is connected with the engine exhaust manifold 12 by the inlet screen assembly 18 of the present invention.

In FIGS. 2 4 the detailed construction of the screen assembly 18 is shown. The assembly includes a housing made up of a frusto-conical tube section 20 connected at its ends with a pair of flanges 22, 24 adapted to, be bolted respectively to the turbine inlet scroll 16 and the engine exhaust manifold 12.

Flange 24 has an outwardly facing recessed portion 26 bordered by an in-turned step 28. Within the recessed portion 26 there is supported a perforated metal plate 30, which acts as a screen to protect the inlet of turbine 14 against the entry of potentially damaging foreign objects; for example, portions of a broken engine valve. The screen 30 and the flange 24 are preferably both circular and are arranged so that there is suffrcient clearance between the outer periphery of screen 30 and the inner diameter of recessed portion 26 to provide for free expansion of the screen with respect to the flange due to its increased temperature during engine operation.

As preferably located, the rear of the periphery of screen 30 is close to, but not necessarily in contact with, step 28 of the flange so as to prevent any foreign matter from passing around the edge of the screen. In the arrangement disclosed, the screen 30 is made generally arcuate in cross section in order to increase its stiffness in resistance to bending. However, if desired, a flat perforated plate could be substituted for the curved plate 30.

Within the tube section and firmly secured thereto, preferably by welding, is a support member 32. Member 32 is made up of a U-shaped bracket element 34, a pair of half-hexagonally shaped screen support elements 36 and a pair of plate-like struts 38; the components being welded together in an assembly. Protruding from the front edge of bracket element 34 is a small lug 40 which extends through the center of plate and is securely welded thereto.

The various elements of the support member coact to solidly support lug within the housing tube section 20 and the lug itself is sufficiently heavy to provide a stiff central support for the perforated plate screen 30. The mass of the lug is, however, made as small as possi- .ble where it contacts the screen to reduce the size of the path for heat transfer through the lug between the plate 30 and the support member 32.

The screen-connected portions of screen support elements 36 comprise six tapering fingers 42 which are radially spaced from and equiangularly disposed around the central lug 40. Fingers 42 are made thin and relatively flexible in a direction radially of the lug 40 but are relatively wide and stiff in a circumferential direction. The fingers have their smaller ends received within elongated openings 44 of the plate 30 at points which are closer to the center of the plate than to its periphery. Rows of small perforations 46 are provided in the plate along both sides of the openings 44.

The structure of fingers 42 makes them stiff in directions transverse to radii extending through them and the lug 40 so that they aid substantially in providing support for the screen 30 in addition to that provided by lug 40. On the other hand, the flexibility of the fingers in a radial direction permits relatively free expansion of the screen's central portion outwardly from the solid central support of lug 40, as may be necessary during transient operating conditions of the engine that cause rapid temperature changes in the screen.

The area of connection of each of the fingers 42 with the screen 30 is made small so that the heat flow path between the screen and the support member through the fingers is minimized. In addition, the reduced heat sink effect remaining at the junctures of the fingers 42 and plate 30 is in part offset by the small perforations 46 which increase the area for heat transfer between plate 30 and the exhaust gases adjacent the said junctures.

In operation, the temperature of exhaust gases passing through the screen 30 varies rapidly as the power output of the engine is changed; for example, by moving the throttle from idle to the full throttle position or vice versa. When the temperature is rapidly increased, the screen is free to expand radially due to the clearance between its periphery and the recessed portion 26 of flange 24. In addition, the flexing of fingers 42 will permit expansion of the central portion of the screen without restraint from the support member 32. While the connection of the screen with the central lug 40 and the six flexible fingers 42 of the support tends to slow the rate of temperature increase slightly at the points of connection, this tendency is minimized by the fact of the small cross-sectional areas of these support elements at the points of connection with the screen as well as by provision of increased heat transfer area at these points. In this way, internal stresses within the screen due to local temperature differences are also minimized.

While the invention has been described by reference to a preferred embodiment, it should be apparent that the inventive concepts disclosed herein could equally well be applied to structures having substantial differences in construction details without departing from the spirit and scope of the invention as defined in the following claims.

We claim:

1. In combination I an internal combustion engine and an exhaust gas driven turbine with passage defining means connecting the inlet of said turbine with the exhaust of said engine,

a perforated metal plate in said passage defining means and extending across the exhaust gas flow path to the turbine inlet, said plate acting as a screen to protect the turbine from potentially damaging particulate matter in the exhaust gases, said plate being subject to damage by internal stresses caused by excessive temperature differentials between various portions thereof, and

a support member secured within said passage defining means and mounting said plate with lateral clearance from said passage defining means to provide for relative expansion thereof, said support member having a stiff primary mounting portion secured to a central portion of said plate and a plurality of radially flexible secondary mounting portions secured to said plate at points radially spaced from said primary mounting portion, said primary and secondary mounting portions having their points of contact with said screen consisting of small projections, each having a small area of contact with said screen member and a limited crosssectional area adjacent said screen member so as to minimize transient temperature differentials in said plate due to heat transfer between said support and said plate.

2. For'use in an internal combustion engine having an exhaust gas driven turbine, a screen assembly adapted to cover the inlet to such turbine to protect the turbine from potentially damaging particulate matter in the exhaust gases, said screen assembly comprising a housing adapted to be mounted at the inlet to the turbine, said housing defining an exhaust gas flow path therethrough,

a perforated metal plate forming a screen and disposed within said housing across the exhaust gas flow path, said plate being subject to damage by internal stresses caused by excessive temperature differentials between various portions thereof, and

a support secured within said housing and mounting said plate within said housing with radial clearance to permit expansion of said plate relative to said housing, said support having a stiff lug secured to a central portion of said plate and a plurality of radially flexible fingers secured to said plate at points spaced radially of said lug, said lug and said fingers each having a small cross-sectional area with minimal mass at and adjacent their points of attachment to said plate so as to minimize temperature differentials in said plate due to heat transfer between said support and said plate.

3. A screen assembly as defined in claim 2 wherein the radial distance of said flexible fingers from said lug is substantially less than the radial distance from said fingers to the periphery of said plate. 

1. In combination an internal combustion engine and an exhaust gas driven turbine with passage defining means connecting the inlet of said turbine with the exhaust of said engine, a perforated metal plate in said passage defining means and extending across the exhaust gas flow path to the turbine inlet, said plate acting as a screen to protect the turbine from potentially damaging particulate matter in the exhaust gases, said plate being subject to damage by internal stresses caused by excessive temperature differentials between various portions tHereof, and a support member secured within said passage defining means and mounting said plate with lateral clearance from said passage defining means to provide for relative expansion thereof, said support member having a stiff primary mounting portion secured to a central portion of said plate and a plurality of radially flexible secondary mounting portions secured to said plate at points radially spaced from said primary mounting portion, said primary and secondary mounting portions having their points of contact with said screen consisting of small projections, each having a small area of contact with said screen member and a limited cross-sectional area adjacent said screen member so as to minimize transient temperature differentials in said plate due to heat transfer between said support and said plate.
 2. For use in an internal combustion engine having an exhaust gas driven turbine, a screen assembly adapted to cover the inlet to such turbine to protect the turbine from potentially damaging particulate matter in the exhaust gases, said screen assembly comprising a housing adapted to be mounted at the inlet to the turbine, said housing defining an exhaust gas flow path therethrough, a perforated metal plate forming a screen and disposed within said housing across the exhaust gas flow path, said plate being subject to damage by internal stresses caused by excessive temperature differentials between various portions thereof, and a support secured within said housing and mounting said plate within said housing with radial clearance to permit expansion of said plate relative to said housing, said support having a stiff lug secured to a central portion of said plate and a plurality of radially flexible fingers secured to said plate at points spaced radially of said lug, said lug and said fingers each having a small cross-sectional area with minimal mass at and adjacent their points of attachment to said plate so as to minimize temperature differentials in said plate due to heat transfer between said support and said plate.
 3. A screen assembly as defined in claim 2 wherein the radial distance of said flexible fingers from said lug is substantially less than the radial distance from said fingers to the periphery of said plate. 